//
// Created by Jisam on 2024/7/28 19:05.
// solve b
#include <bits/stdc++.h>

#define PSI pair<string,int>
#define PII pair<int,int>
#define PDI pair<double,int>
#define PDD pair<double,double>
#define VVI vector<vector<int>>
#define VI vector<int>
#define VS vector<string>

#define PQLI priority_queue<int, vector<int>, less<int>>
#define PQGI priority_queue<int, vector<int>, greater<int>>
using u32 = unsigned;
using i64 = long long;
using u64 = unsigned long long;

using namespace std;


void solve() {
    string s;
    cin >> s;
    int n = s.size();
    i64 ans = 0;
    for(int i = 0 ; i <  n /2 ; i ++){
        if(s[i] != s[n - i - 1]){
            ans += min(abs(s[n - i  - 1] - s[i]),26 - abs(s[n - i  - 1] - s[i]));
        }
    }
    cout << ans;
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int T = 1;
//    cin >> T;
    while (T--) solve();
//    cout << "\n"[];
    return 0;
}